Agrobacterium rhizogenes is the causal organism of what has been termed "the hairy root disease" in a number of species of higher plants. A. rhizogenes can be isolated from the soil, and is a species of agrobacterium which has the following characteristics: aerobic, rod-shaped (0.8.times.1.50-30 micron), one to four peritrichous flagella, Gram negative, and nonspore forming. The common species are A. tumefaciens, which is tumor-causing; A. rhizogenes, which causes hairy-root disease; and A. radiobacter, which is nonpathogenic.
The potential of using A. rhizogenes to the benefit of man was mentioned in an article entitled, "Studies on Infectious Hairy Root of Nursery Apple Trees," Journal of Agricultural Research, Vol. 41, No. 7, pp. 507-540, A. J. Riker et al. The authors state at 537, "In preliminary experiments cuttings or layers of certain plants treated with the hairy-root organism have rooted sooner and more vigorously than those untreated. These results suggest the possibility of using this organism to stimulate root production in the propagation of certain plants. More work is necessary before conclusions can be drawn." Despite this invitation, A. rhizogeneshas not been actively pursued to the benefit of man, and remains regarded as an undesired pathogen.